test_post_please_ignorefandomcom-20200215-history
Frame
2016 Stiffness Test Objective: Perform chassis stiffness test to validate frame design and construction. ANSYS model requires some vague simplifications to make it feasible. This includes replacing the suspension with excessively strong welded joints, squaring off all tubing bends, and replacing the engine with a box made of tubing. The model also does not include any gussets or other vehicle components which may add to overall frame stiffness. In order to put some real world number to the chassis stiffness this test was undertaken. Apparatus McLaughlin Hall Machine Shop is the proud owner of a large torsion table. I decided to use this to do my torsion test since it has a load cell, pivot, jack and a very stiff table already prepared. Plates were made to fit the current centre-lock wheel packages to allow for a full chassis test. A large arm was welded from 3”x0.125 square tubing for the front end. This connected to the pivot. The rear wheel plates were mounted (welded) directly to the table. = Method Once the car was painstakingly installed a number of dial indicators were magnetically positioned. One was placed on an arm built into the pivot which gave the motion of the pivot shaft with respect to the table. Others were placed at the front and rear of the car (left and right, on the underneath of the frame a set distance apart). Finding the zero or neutral position in the setup proved difficult since the weight of the system was quite high. The front pivot arm was levelled and this position was used to tare the force gauge. This invalidates any low torque numbers where much of the force was put into loading up the weight of the system. Also the low force readings include compression in washers, etc. A digital angle finder was used as a rough guide for measurements. 2016 Frame Review/ Recommendation Alignment of roll hoops to other tubing results in more complex jigging due to difference in tubing sizes. These sections have a 1/16 difference in height. Creating an artificial axis in the roll hoop tube to make the lower faces line up will simplify jigging. Particularly here where it should sit flat on the table. Moving toward more bent tubes instead of mitred and welded joints add simplicity, save time and increases frame accuracy. The recommended areas are marked in red. = Torsion Test = Frame stiffness test showed that the weakest sections are likely the front and rear. It probably gets worse under higher-than-test loading. This is contrary to what I was led to believe about the front being the strongest section and the middle being the weakpoint. Cannot confirm if the X brace added enough stiffness to change this but it is unlikely. I think the two small grey tubes in the front changed its strength significantly. Must consider stiffening the front with a new design or adding in larger tubes in future. Overall frame stiffness is probably sufficient. It should ideally remain between 1500 and 2000 for the load range it will experience. Ideally stiffness will become linear at some load. Suspension is not the weak point of this system, so I do not recommend going to push rods for the sake of tuning or stiffness. Frame stiffness is lower than suspension at this point. Marginal frame (and therefore chassis) improvements can be made with proper application of Pareto principle. The results from the ANSYS simulation showed that the frame stiffness was 1341 Nm/deg at any applied load. This value lands somewhere between the tested frame stiffness and the tested chassis stiffness with deadshocks. This makes sense because the ANSYS simulation is created with a fictional high-stiffness triangulated A-arm setup. Technically it is a chassis test but with a fictional suspension that is quite strong. Our testing proves that our real A-arms are quite strong as well with some interesting movement under loading. The ANSYS model therefore shows a hybrid of the frame and chassis testing, which falls between the actual frame and chassis values. The modeling is typically done with one fixed point at a rear wheel, with cross wheels allowing for movement in the horizontal plane, and a load applied at one front wheel. Since the rear end was rigidly fixed in all directions with minor deflection in the lateral direction I modified the model to allow for no movement at the rear wheels. This resulted in an increase of around 12% stiffness. Future torsion tests should have a rear end which can move in the horizontal plane. Attempts to model the front rotational arm of the torsion table setup more accurately gave odd results. = CG locations: = For future I would like to go with rear subassembly. Here is a pic from 2014 that Dalton had dreamed up. I would like to see the blue tube connecting the frame to subframe as bolted for quick removal. Take engine out in 6 bolts or less.